1. Field of the Invention
This invention relates generally to an underwater soil erosion prevention system, and a method of deploying the same using an inflatable, rollable array.
2. Description of the Related Art
Devices used to prevent underwater soil erosion and cause soil deposition are known. Typical devices include buoyant frond elements or artificial seaweed anchored underwater in the area in which soil erosion (i.e., seafloor scour) is to be prevented. These devices operate by exerting a viscous drag on the underwater current, which reduces the velocity of the current and of soil particles transported by the current to a level where the soil particles settle out of the current and are deposited around the soil erosion prevention device.
For example, U.S. Pat. No. 5,176,469 to Alsop discloses a structure comprising a continuous sequence of buoyant fronds arranged side by side, each of which is attached to a base line wherein the line is folded back and forth to form frond sections. Each section is anchored to the ground through the base line.
Another example of an underwater soil erosion prevention system is shown in U.S. Pat. No. 4,722,639 to Alsop. In this system, an open grid mat structure is used as a base to attach a number of randomly overlapping elongate buoyant frond elements. The open grid mat structure requires the grid lines to be at least nine inches (9") apart from one another in practice. Spacing the grid lines, and thus frond elements, so far apart from one another limits the viscous drag exerted on the current and, thus, the structure's soil erosion prevention capabilities. In addition, the open grid mat disclosed in the foregoing patent is not adapted to be efficiently manufactured and deployed. A need exists for an easily manufactured and deployed device to exert a maximum amount of viscous drag (i.e., maximum wetted surface area) on the current to maximize soil erosion prevention.
Underwater soil erosion prevention systems must be deployed where they are to prevent soil erosion, which is often at great depths underwater. Deployment of such systems is difficult and costly. U.S. Pat. No. 5,176,469 to Alsop discloses an example of a deployment system in which an underwater soil erosion prevention system in the form of a continuous sheet folded back and forth from side to side is packed in a box-like dispenser with the sections in a compact state. When in the desired location for deployment, the leading edge of the soil erosion prevention system is pulled out and anchored down, and the box-like dispenser is advanced such that the compacted soil prevention system is thereby withdrawn and unpacked. One problem with this deployment system is that it requires divers to physically move the dispenser (which can be quite heavy) underwater, a difficult and time consuming process.
Another example of a deployment system is shown in U.S. Pat. No. 4,722,639. One end of each frond element disclosed therein is attached to an open grid mat structure, while the other end of each such frond element is allowed to float free. The open grid mat structure disclosed therein is rolled up, placed underwater in the desired location and physically unrolled by the divers deploying the system. Because of the loose individual frond elements, rolling up and unrolling this mat structure is difficult. Even if a net or other restraining device is used to restrain the unattached frond ends, this system is still difficult to roll because the frond elements disclosed therein are bulky and do not naturally lay flat. Deployment of this structure underwater by unrolling it is also difficult and labor intensive work.
A need exists for an easier deployment system to deploy underwater soil erosion prevention systems. Therefore, it is desirable to have a soil erosion prevention system which is effective in the field to prevent underwater soil erosion and a system for easily deploying it underwater.